复合管液压成形装置及残余接触压力预测

针对现有复合管制造工艺中存在的问题，研制开发了一种焊接不锈钢衬里复合管液压成形装置，介绍了该装置液压成形系统的工作原理及技术特点。阐述了复合管液压成形过程的原理，并采用弹塑性理论分析了其在液压成形过程中内管及外管的应力应变状态。推导出了复合管残余接触压力与成形压力之间关系的理论计算公式，通过实验对公式进行了验证。结果表明该装置结构及其计算方法适于工程应用。     

双金属复合管液压成形压力的计算

根据基本假设，建立双金属复合管的材料模型及力学模型。采用弹塑性理论，分析双金属复合管液压成形过程中内管及外管的应力应变状态。利用变形协调条件，得出液压力Pi与复合管内外管之间残余接触压力Pe^*的计算公式，给出液压成型压力的最大值与最小值，并通过试验验证理论公式的准确性。双金属复合管复合成形时要想获得残余接触压力，外层管材料屈服强度必须大于内层管材料屈服强度或强化后的应力值。     

自紧密封不锈钢衬里复合管液压胀合研究

研制开发了一种径向自紧密封式不锈钢衬里复合管液压胀合成形装置。讨论了复合管液压胀合成形过程的原理,并采用弹塑性理论分析了其在胀合成形过程中内管及外管的应力应变状态。利用变形协调条件,得出了胀合压力p_e与复合管内外管之间残余接触压力p_r~*的理论计算公式,并通过试验对公式进行了验证。结果表明该装置结构及其计算方法均可适于工程应用。     

基于Dynaform三通管液压成型分析

提出改进液压成型工艺,并通过Dynaform软件仿真及实际生产验证。该方法舍弃了通常管材液压成形中所需的超高压供给系统以及平衡冲头,进而大大降低设备费用。在验证工艺正确基础上,通过Dynaform软件仿真分析影响三通管液压成型因素。仿真模拟分析为模具设计方案和液压成形工艺方案设计提供了科学的依据,提高了设计效率。     

基于径压胀形确定管材的摩擦因数

摩擦对管材液压成形有极大的影响,管材摩擦因数的确定是一项极其重要的工作。在分析比较现有测试方法的基础上,基于径压胀形原理及其变形规律提出确定管材液压成形胀形区摩擦因数的新模型。该模型以恒定内压力下圆形管材径压胀形成方形断面后,以断面对角线长度差作为确定摩擦因数的测量指标。对比对角线长度差的有限元数值模拟结果及实测结果,以此确定管材液压成形时胀形区的摩擦因数。对低碳钢及不锈钢管的有限元数值模拟分析表明：对角线长度差与摩擦因数及内压力均成指数关系,该长度差对摩擦力很敏感且可方便测量,也可作为针对管材液压成形胀形区润滑剂特性的评定指标。所提出的新模型具有简单、实用等优点。     

An analysis of hydroforming of longitudinally curved boxes with regular polygonal cross-section

A new kinematically admissible velocity field is suggested for the upper-bound solution of hydroforming of longitudinally curved boxes with regular polygonal cross-section. In order to maintain the uniform wall thickness the back-up fluid pressure is controlled to vary with respect to the punch position during the hydroforming process. The pressure vs punch stroke curves for various process conditions are determined from theoretical analysis. The effects of punch shape, work-hardening exponent, drawing ratio and friction are then analysed and discussed. Experiments are carried out in a hydroforming press according to the computed pressure vs punch stroke curves. The hydroformed specimens have shown very little thickness variation within a 5% range. Thus, the validity of the assumption of uniform wall thickness has been confirmed. The flange deformation from the computation is found to be in good agreement with the experimental observation. When the computed reference curve of pressure vs punch stroke relation has been used, no defect, i.e. no necking or no wrinkling has been observed in the experimental specimens. It has been shown that the present method of analysis can be effectively used for the hydroforming process design of longitudinally curved boxes with regular polygonal cross-section.     

An analysis of hydroforming of regular polygonal boxes

A new kinematically admissible velocity field is suggested for the upper-bound solution of three-dimensional hydroforming of regular polygonal boxes. In order to maintain the uniform wall thickness a back-up fluid pressure is controlled to vary with respect to the punch position during the hydroforming process. Thus the pressure vs punch stroke curves for various process conditions are determined from theoretical analysis. The effects of the work-hardening exponent, drawing ratio and friction are then analyzed and discussed. Control of the hydroforming pressure with respect to the punch stroke is shown to be very important for proper design of the process.     

Die shape design for T-shape tube hydroforming

In this paper, two design methods for T-shape tube hydroforming dies are proposed, namely, the extrusion-cutting-fillet method (ECFM) and the intersection-fillet method (IFM). Simulations on hydraulic expansion and axial feeding of T-shape tube hydroforming with two dies using the program DEFORM-3D were performed. The influence of the two dies on workpiece formability of T-shape tube hydroforming was examined. Experiments were carried out with SUS304 stainless steel tube at room temperature. A qualified product of T-shape tube, without wrinkling or bursting, was obtained using the die designed by the IFM method.     

Reliability analysis of stainless steel/carbon steel double-layered tube on the basis of thermal deformation behavior

The thermal expansion of pipes depends on both the temperature of the pipe and the expansion coefficient of the piping material at the operating temperature. In the case of a double-layered tube consisting of two different tube materials, the thermal deformation behaviors are dependent on the relative tube sizes, thermal expansion coefficients, and the mechanical properties of the inner and outer tubes. For the safe and reliable application of double-layered tubes that are fabricated by hydroforming, the thermal stress in circumferential direction and the gap between the inner and outer tubes need to be analyzed over a wide range of temperatures (?50°C～200°C). As it is difficult to measure the thermal stress and the gap between tubes at operating temperature, this study has analytically investigated the thermal deformation behavior of a double-layered tube. From the analytical model, the effect of hydraulic pressure, residual stress, and the relative sizes of the inner and outer tubes on the resultant thermal deformation, such as the circumferential thermal stress and the gap between inner and outer tubes, has been analyzed. The analytical results provide a theoretical basis for determining the reliable operating temperature of double-layered tubes.     

On the tube hydroforming process using rectangular,trapezoidal, and trapezoid-sectional dies: modeling and experiments

It is generally known that the contact between tube and die, in the case of tube hydroforming process, leads to the appearance of friction effects. In this context, there are many different models for representing friction and many different tests to evaluate it. In the present paper, the pin-on-disk test has been used and the theoretical model of Orban-2007 has been chosen and developed to evaluate friction coefficient. The main goal is to prove the capacity of theoretical model to present the friction conditions in comparison with the pin-on-disk test. From the Orban model, values of 0.05 and 0.25 of friction coefficient have been found under lubricated and dry tests, respectively. On the other hand, by the classical pin-on-disk test, other values were experimentally obtained as friction coefficient at the copper/steel interface. In the case of pure expansion hydroforming, based on an internal pressure loading only, a “corner filling” test has been run for tube hydroforming. Both dry and lubricated contacts have been considered. Various configurations and shapes have been studied such as the rectangular, trapezoidal, and trapezoid-sectional dies. Finite element simulations with 3D shell and 3D solid models have been performed with different values of friction coefficients. From the main results, it was found that the critical thinning occurs in the transition zone for the square and rectangular section die and in the sharp angle for the trapezoidal and trapezoid-sectional die. The comparison between numerical data and experimental results shows a good agreement. Moreover, the thickness distribution along the cross section is relatively consistent with those measured for the 3D shell model; however, the 3D solid models do not provide a realistic representation of the thickness distribution in the shaped tube. Finally, the results obtained from the theoretical model were more efficient than the results obtained from the pin-on-disk test.     

Bursting failure prediction in tube hydroforming using FLSD

In tube hydroforming, circular components are hydrobulged or hydroformed from tubular blanks with internal pressure and simultaneous axial loading. Thus the tube can be fed into the deformation zone during the bulge operation allowing more expansion and less thinning without any defects such as wrinkling, buckling, and bursting. By contrast with the buckling and the wrinkling, the bursting is generally classified as an irrecoverable failure mode. Hence in order to obtain the sound hydroformed products, it is necessary to predict the bursting behavior and to analyze the effects of process parameters on this failure condition in hydroforming processes. In this study, a forming limit stress diagram (FLSD) is constructed by plotting the calculated principal stresses based on the local necking criterion. Using the theoretical FLSD, we carry out the numerical prediction of bursting failure in a hydroforming process, which usually has non-linear strain path. Finite element analyses are carried out to find out the state of stresses during simple hydroforming operation, in which the FLSD is utilized as the forming limit criterion for assessment of the initiation of necking, and influences of the material parameters on the formability are investigated. In addition, the numerical results obtained from the FEM combined with the FLSD are confirmed with a series of bulge tests in view of bursting pressure and show a good agreement. Consequently, it is shown that the theoretical and numerical approach to bursting failure prediction proposed in this paper will provide a feasible method to satisfy the increasing practical demands for assessment of the forming severity in hydroforming processes.     

Simulation of dissimilar tailor-welded tubular hydroforming processes using EAS-based solid finite elements

Developments in the numerical simulation of the hydroforming process of tubular metallic components, tailor-welded before forming, are presented. Both technologies, tailor-welded joining operations and hydroforming processes, are well known in industry, although most commonly separately used. Tailor-welded joining operations are usually encountered in plain sheets, subsequently formed by stamping. Tube hydroforming processing, on the other hand, is frequently associated with parts consisting of uniform thickness, material properties, and dimensions. The present analysis focuses on the influence of process parameters, such as the position of the weld-line and initial thickness values, in the innovative process of combining tailor-welded tubes (with distinct thickness values) and hydroforming. Particular attention is posed on the relation of imposed axial displacement vs. imposed hydraulic pressure into the tube, forming parameters that are not known a-priori in the manufacturing of a new part. Another point of practical interest is the numerical simulation of the weld-line movement, after forming is complete. The finite element method is directly employed in the numerical simulation by means of innovative solid elements suited for incompressibility applications, and included by the authors into the commercial program ABAQUS as user-elements. The obtained results can then lead to a better understanding, along with design tools, for the process of hydroforming of tailor-welded tubular parts, accounting for dissimilar thickness of the basic components.     

冷却油路型射流管式伺服阀的热力学研究

 射流管式电液伺服阀因抗污染能力强、灵敏度高、失效对中等特点,被广泛应用于航天、航空、船舶等领域。介绍了冷却油路型射流管式电液伺服阀的结构原理,建立了稳态传热过程的热流量方程。利用有限元软件ANSYS 对冷却油路型射流管式电液伺服阀进行了热力学分析,并分析了力矩马达内部温度分布以及热梯度等物理量。试验验证了冷却油路型射流管式电液伺服阀的冷却效果,为冷却油路型射流管式伺服阀的结构设计、热力学研究提供了理论依据。     

Study of Hydroforming Lubricants with Overbased Sulfonates and Friction Modifiers

Due to the high cost of hydroforming equipment, attempts have been made to model this process using bench testing. While tensile and twist compression tests have yielded promising results, they do not simulate any single metal forming process. In this study we investigated the use of expansion zone, guiding zone, and twist-compression tests to simulate hydroforming processes and evaluated various overbased sulfonates and organic friction modifiers performance. The amorphous overbased magnesium sulfonate improved the performance of the hydroforming oil in the expansion zone and provided no harm in the guiding zone, while the crystalline overbased calcium sulfonate provided no harm in the expansion zone and improved performance in the guiding zone. It was found that the friction modifiers tested display an antagonism, where, as the expansion zone performance increased, the guiding zone performance decreased. Additionally, we found in twist-compression testing that the initial coefficient of friction displayed a small correlation with the guiding zone test (from r = 0.26–0.47), while the failure time displayed a small correlation with the expansion zone test (r = 0.36–0.40).     

A study of process and die design for ball valve forming from stainless steel tube

In this paper, two process and die design methods for ball valve forming from stainless steel tubes are compared: one is the tube hydroforming method (THFM), and the other is the tube nosing method (TNSM). Simulations on hydraulic expansion, axial feeding, and tube nosing of the ball shell forming with the two methods using the program DEFORM-3D are carried out. The influence of the two methods on workpiece formability and wall thickness distribution of ball valve forming is examined. A tube nosing experiment is carried out with a SUS304 stainless steel tube at room temperature. An accepted product of ball valve satisfying the industrial demand is obtained using TNSM.     

Numerical analysis and design for tubular hydroforming

To get an optimum deformation path for tubular hydroforming, the hydroforming limit of isotropic and anisotropic tubes subjected to internal hydraulic pressure, independent axial load or torque is firstly proposed based on the Hill's general theory for the uniqueness to the boundary value problem and compared with those of the conventional sheet forming. The influences of the deformation path, the material properties and the active length–diameter ratio on the nucleation and the development of wrinkling during the free tubular hydroforming are also investigated. The above theory is used as a criterion and implemented with some new functions in our ITAS3D, an in-house finite element code for simulating the sheet forming, to control the materials flow and to prevent the final failure modes from occurring. Finally, the tubular hydroforming of an automobile differential gear box is taken as an example to show the efficiency and usefulness of the algorithm.     

内高压成形机理与关键技术

在中国国家杰出青年科学基金资助项目“镁合金热态液力成形技术”、中国国家自然科学基金资助项目“轻体件高内压液力成形机理的研究”、“管材热态内压成形新方法及其机理研究”和“激光拼焊管内高压成形机理”、以及中国教育部高等学校博士学科点专项科研基金资助项目“镁合金热态内高压成形机理研究”共同资助下,开展内高压成形机理及关键技术研究,在内高压成形塑性变形规律、起皱和破裂等失稳行为、提高成形极限和降低成形压力方法,以及液力胀接、热态内压成形和拼焊管内高压成形等方面取得重要进展,并在汽车和航天等领域实现内高压成形技术产业化应用,报告上述研究的理论和工程体系。 根据塑性变形特点,将内高压成形分为变径管内高压成形(IHPF of TPVD)、弯曲轴线管内高压成形(IHPF of TPCA)和多通管内高压成形(IHPF of TPB/BT)等3类,提出IHPF of TPVD由充填、成形、整形等步骤组成,IHPF of TPCA由弯曲、预成形、内高压成形等步骤组成,IHPF of TPB/BT由胀形、补料、整形等步骤组成。以此为出发点,通过实验和理论分析,研究IHPF塑性变形规律与失稳行为。     

脉动液压成形技术与设备

介绍脉动液压成形技术的成形原理、工艺特点及应用领域。从工艺和材料两方面对脉动液压成形提高材料成形能力的机理进行研究,试验证明脉动载荷一方面能够促进管材液压成形时的补料、降低摩擦力的阻碍作用并利用成形过程中小褶皱的出现与消失提高变形的均匀性;另一方面,对于奥氏体不锈钢,脉动载荷可以增强形变过程中的相变增塑效应,从而提高其成形性。自主设计并研制出能实现工业化生产需求的自动化程度高的脉动液压成形设备,为该项技术在汽车、航空及航天制造领域中的推广和应用提供重要的理论指导和实践探索。     

Hydroforming of aluminum extrusion tubes for automotive applications. Part II: process window diagram

Based on the mathematical formulations for predicting forming limits induced by buckling, wrinkling and bursting of free-expansion tube hydroforming, a theoretical “Process Window Diagram” (PWD) is proposed and established in this paper. The theory developed in the first part of the present work was formulated within the context of free-expansion tube hydroforming with both combined internal pressure and end feeding. The PWD is designed to provide a quick assessment of part producibility for tube hydroforming. The predicted PWD is validated against experimental results conducted for 6260-T4 60×2×320 (mm) aluminum tubes. An optimal loading path is also proposed in the PWD with an attempt to define the ideal forming process for aluminum tube hydroforming. Parametric studies show that the PWD has a strong dependency on tube geometry, material property and process parameters. To the authors’ knowledge, this is the first attempt that a PWD is being formulated theoretically. Such a concept can be advantageous in deriving design solutions and determining optimal process parameters for tube hydroforming processes.     

Investigation of T-Shape Tube Hydroforming with Finite Element Method

In this paper, the finite element method is used to investigate the cold hydroforming process of a T-shape tube. A series of simulations on hydraulic expansion, axial feeding and the counterforce of the tubes was carried out using the program DEFORM-3D. The influences of the process parameters such as the internal pressure, the fillet radius, and counterforce on the minimum wall thickness of formed tube are examined. A suitable range of the process parameters for producing an acceptable T-shape tube that fulfils the industrial demand was also found. ID="A1"Correspondance and offprint requests to: Dr C.-T. Kwan, Department of Mechanical Manufacturing Engineering, National Huwei Institute of Technology, 64 Wunhua Road, Huwei, Yunlin, 632, Taiwan. E-mail: ctkwan@sunws.nhit.edu.tw